OBD Guide
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U2104

Controller Area Network Bus Reset Counter Overrun

U2104 is an OBD-II diagnostic trouble code meaning: Controller Area Network Bus Reset Counter Overrun. Common causes: poor contact in can bus connectors, short circuit in can circuit. Estimated repair cost: $6–56.

Severity
🔴 High
Can you drive?
Do not drive — repair immediately
Approx. repair cost
$6–56 (est.)

Symptoms

  • Check Engine Light Is On
  • Intermittent operation of electronic systems
  • Lost connection with some modules
  • Spontaneous factory resets

Causes

  • Poor contact in CAN bus connectors
  • Short circuit in CAN circuit
  • Malfunction of one of the network modules
  • Problems with module power supply
  • Damage to CAN wire shielding

How to Fix

  1. Check battery and generator voltage
  2. Inspect the CAN bus connectors and wires for damage
  3. Check the resistance of the CAN wires (typically 60 ohms between CAN-H and CAN-L)
  4. Disable the modules one by one to identify the faulty one.
  5. Check the quality of module grounding

Related codes

U0100U0121U0155

FAQ

What does the U2104 code mean?

U2104 is an OBD-II diagnostic trouble code that indicates: Controller Area Network Bus Reset Counter Overrun

What causes a U2104 error code?

The most common causes of U2104 include: Poor contact in CAN bus connectors; Short circuit in CAN circuit; Malfunction of one of the network modules; Problems with module power supply.

How do I fix a U2104 diagnostic trouble code?

To fix U2104: Check battery and generator voltage. Inspect the CAN bus connectors and wires for damage. Check the resistance of the CAN wires (typically 60 ohms between CAN-H and CAN-L). For a complete diagnosis, use an OBD-II scanner.

Is it safe to drive with U2104?

Do not drive — repair immediately

How much does it cost to fix U2104?

The estimated repair cost for U2104 is $6–56. Actual cost depends on your vehicle, location, and labor rates.

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See also: Russian version · NationStat